About 69 percent of American adults are overweight or obese, and more than four in five people say they are worried about obesity as a public health problem.

But a recent poll conducted by NPR, the Robert Wood Johnson Foundation and the Harvard School of Public Health revealed a curious schism in our national attitudes toward obesity: Only one in five kids had a parent who feared the boy or girl would grow up to be overweight as an adult.

Put another way, assuming current trends persist, parents of 80 percent of American children think all these kids will somehow end up being among the lucky 31 percent of adults who are not overweight.

Tali Sharot is a neuroscientist at University College London who studies why large numbers of people — faced with a large number of different kinds of risks — believe they and their family members will dodge the odds.

"People underestimate their likelihood of experiencing all kinds of negative events, including medical illnesses," she says. "And they do that for their family members as well. So not only do we think we are immune more than other people, we think that our kids are also more immune than other kids."

Psychologists have noted the phenomenon in a number of domains that have nothing to do with health: Most people getting married believe they will stay married forever, for example, even though the divorce rate is around 50 percent.

"The optimism bias is our tendency to overestimate our likelihood of experiencing positive events in our lives, and underestimating the likelihood of experiencing negative events in our lives, such as divorce or cancer," Sharot says.

Psychologist Neil Weinstein helped to discover the bias when he asked students about the likelihood of different events in their lives.

He found that the students believed they were more likely than their classmates to find a job they loved or get an above-average salary. But they believed their classmates were more likely than they were to commit suicide or to develop a drinking problem.

More recent research by Sharot and others has found that we not only have rose-colored glasses about our future, and the future of our kids, but that we actually discount negative information.

"If someone says, 'My likelihood of suffering from cancer is about 20 percent,' and we say, 'You know, the average likelihood is actually worse — it's about 30 percent,' the next time around when you ask them, they say, 'Well, I still think my estimate of suffering from cancer is about 22 or so,' " Sharot said.

But if people don't believe bad news applies to them, they seem readily willing to take in positive news. People readily change their views when you tell them they've been too pessimistic.

"If they start off saying, 'My likelihood of suffering from cancer,' for example, 'is 40 percent,' and you say, 'You know, the average likelihood is better — it's only 30 percent,' the next time around they would say, 'Well, in that case, my likelihood is maybe 32 or so,' " says Sharot, who is the author of The Optimism Bias: A Tour of the Irrationally Positive Brain.

In a series of brain experiments, Sharot has identified two areas in the frontal lobe — the left inferior frontal gyrus and the right inferior frontal gyrus — that appear to regulate how people process good and bad news. When she temporarily disables the normal functioning of the brain areas using a magnetic field, Sharot finds that the bias disappears. People stop being overly optimistic. They start to take risks seriously.

Now, this bias isn't a brain defect. In fact, multiple studies have shown the optimism bias produces a variety of positive life outcomes. We do better in life when we expect to do well.

The trouble arises when it comes to major public health problems like childhood obesity.

Sharot suggests that these results have an implication for how public health concerns over obesity are communicated: "If the message is, 'You know, there is a high likelihood of your kid being obese and that would lead to all these negative things,' people will tend to shut down and say, 'This is not related to me,' " she says.

A more effective technique might take advantage of the optimism bias.

In other words, don't tell parents obesity is a major public health problem. Tell them how family dinners and exercise can turbocharge their kids, and you might get them to think, "Yeah, I can totally see my kid being a superstar!"

Today in Your Health, we'll focus on the challenge of getting kids to eat the right food. We start with our own contradictory views on obesity. This story grows out of an unexpected result of a recent survey. NPR conducted the poll with the Robert Wood Johnson Foundation and the Harvard School of Public Health. It explored attitudes towards childhood obesity. And the poll found many Americans worried about growing waistlines. That's no surprise, yet many Americans are also comfortable with their own family's diet and lifestyle.

NPR science correspondent Shankar Vedantam asked how both findings could be true.

SHANKAR VEDANTAM, BYLINE: Lots of Americans are concerned about childhood obesity. But the parents of four out of every five children in our poll said they weren't worried about their kids.

I called up Tali Sharot, a neuroscientist at University College London. She studies this kind of paradox. Without telling her what we found, I asked what she expected us to find.

TALI SHAROT: I suspect that what you found is that people highly underestimate the likelihood of their kids being obese.

VEDANTAM: How would you know that? How did you know that was the case? Why would you have predicted that?

SHAROT: People underestimate their likelihood of experiencing all kinds of negative events, including medical illnesses. And they do that for their family members as well. So not only do we think we are immune more than other people, we think that our kids are also more immune than other kids.

VEDANTAM: Sharot and others have called this an optimism bias.

SHAROT: The optimism bias is our tendency to overestimate our likelihood of experiencing positive events in our lives, and underestimating the likelihood of experiencing negative events in our lives, such as divorce or cancer.

VEDANTAM: Three decades ago, psychologist Neil Weinstein discovered the bias when he asked students about the likelihood of different events in their lives. He found that the students believed they were more likely than their classmates to find a job they loved or get an above-average salary. But they believed their classmates were more likely than they were to commit suicide or to develop a drinking problem.

More recent research has found we not only have rose-colored glasses about our future, and the future of our kids, we actually discount negative information.

SHAROT: If someone says, my likelihood of suffering from cancer is about 20 percent. And we say, you know, the average likelihood is actually worse. It's about 30 percent. The next time around when you ask them, they say, well, I still think my estimate of suffering from cancer is about 22 or so.

VEDANTAM: In other words, they don't change their mind very much, but it's different when you give them good news. People readily change their views when you tell them they've been too pessimistic.

SHAROT: If they start off saying, my likelihood of suffering from cancer, for example, is 40 percent. And you say, you know, the average likelihood is, is better - it's only 30 percent. The next time around they would say, well, in that case, my likelihood is maybe 32 or so.

VEDANTAM: In a series of experiments, Sharot has identified a region in the brain that seems to be responsible for this bias. She temporarily disables this region using a magnetic field and then asks people what they think. The bias disappears. People stop being overly optimistic. They start to take risks seriously.

Now this bias isn't a brain defect. In fact, multiple studies have shown the optimism bias produces a variety of positive life outcomes. We do better in life when we expect to do well. The trouble arises when it comes to major public health problems like childhood obesity.

SHAROT: What we find is that people tend to ignore bad news. And they tend to think about bad news as unrelated to themselves. So if the message is, you know, there's a high likelihood of your kid being obese and that would lead to all these negative things, people will tend to shut down and to say, this is not related to me.

VEDANTAM: So what can be done? Sharot said a more effective technique would be to take advantage of the optimism bias. Don't tell parents obesity is a major public health problem. Tell them how family dinners and exercise can turbocharge their kids. And they'll think, yeah, I can totally see my kid being a superstar.